2005 Microchip Technology Inc. DS21893B-page 13
MCP73861/2
4.0 DEVICE OVERVIEW
The MCP7386X family of devices are highly advanced
linear charge management controllers. Refer to the
functional block diagram. Figure 4-2 depicts the opera-
tional flow algorithm from charge initiation to
completion and automatic recharge.
4.1 Charge Qualification and
Preconditioning
Upon insertion of a battery or application of an external
supply, the MCP7386X family of devices automatically
performs a series of safety checks to qualify the
charge. The input source voltage must be above the
Undervoltage Lockout (UVLO) threshold, the enable
pin must be above the logic-high level and the cell tem-
perature must be within the upper and lower thresh-
olds. The qualification parameters are continuously
monitored. Deviation beyond the limits automatically
suspends or terminates the charge cycle. The input
voltage must deviate below the undervoltage lockout
stop threshold for at least one clock period to be con-
sidered valid.
Once the qualification parameters have been met, the
MCP7386X initiates a charge cycle. The charge status
output is pulled low throughout the charge cycle (see
Table 5-1 for charge status outputs). If the battery
voltage is below the preconditioning threshold (V
PTH
)
the MCP7386X preconditions the battery with a trickle-
charge. The preconditioning current is set to approxi-
mately 10% of the fast charge regulation current. The
preconditioning trickle-charge safely replenishes
deeply depleted cells and minimizes heat dissipation
during the initial charge cycle. If the battery voltage has
not exceeded the preconditioning threshold before the
preconditioning timer has expired, a fault is indicated
and the charge cycle is terminated.
4.2 Constant Current Regulation –
Fast Charge
Preconditioning ends, and fast charging begins, when
the battery voltage exceeds the preconditioning thresh-
old. Fast charge regulates to a constant current (I
REG
),
which is set via an external resistor connected to the
PROG pin. Fast charge continues until the battery volt-
age reaches the regulation voltage (V
REG
), or the fast
charge timer expires; in which case, a fault is indicated
and the charge cycle is terminated.
4.3 Constant Voltage Regulation
When the battery voltage reaches the regulation volt-
age (V
REG
), constant voltage regulation begins. The
MCP7386X monitors the battery voltage at the V
BAT
pin. This input is tied directly to the positive terminal of
the battery. The MCP7386X selects the voltage regula-
tion value based on the state of the V
SET
. With V
SET
tied to V
SS
, the MCP73861 and MCP73862 regulate to
4.1V and 8.2V, respectively. With V
SET
tied to V
DD
, the
MCP73861 and MCP73862 regulate to 4.2V and 8.4V,
respectively.
4.4 Charge Cycle Completion and
Automatic Re-Charge
The MCP7386X monitors the charging current during
the Constant-voltage regulation mode. The charge
cycle is considered complete when the charge current
has diminished below approximately 8% of the
regulation current (I
REG
) or the elapsed timer has
expired.
The MCP7386X automatically begins a new charge
cycle when the battery voltage falls below the recharge
threshold (V
RTH
), assuming all the qualification
parameters are met.
4.5 Thermal Regulation
The MCP7386X family limits the charge current based
on the die temperature. Thermal regulation optimizes
the charge cycle time while maintaining device reliabil-
ity. If thermal regulation is entered, the timer is automat-
ically slowed down to ensure that a charge cycle will
not terminate prematurely. Figure 4-1 depicts the
thermal regulation profile.
FIGURE 4-1: Typical Maximum Charge
Current vs. Die Temperature.
4.6 Thermal Shutdown
The MCP7386X family suspends charge if the die tem-
perature exceeds 155°C. Charging will resume when
the die temperature has cooled by approximately 10°C.
The thermal shutdown is a secondary safety feature in
the event that there is a failure within the thermal
regulation circuitry.
0
200
400
600
800
1000
1200
1400
0 20 40 60 80 100 120 14
Die Temperature (° C)
Maximum Charge Current (mA)
Minimum
Maximum
